Chyba
to deliver Bunyan Lecture on search for life in outer
space

Are we
alone? Stanford Professor Christopher Chyba, who also
holds the Carl Sagan Chair for the Study of Life in
the Universe at the SETI Institute in Mountain View,
Calif., will explore that topic at 7:30 p.m. Monday,
April 21, in Braun Auditorium of the Mudd Chemistry
Building on the Stanford campus. Chyba will deliver
the 23rd annual Bunyan Lecture, hosted by the
Astronomy Program in the Department of Physics. His
talk, titled "The 21st-Century Search for
Extraterrestrial Life," is free and open to the
public.

"Whether
there is other life is one of the great scientific
questions," says Chyba, associate professor
(research) in Stanford's Department of Geological and
Environmental Sciences. He also is co-director of the
Center for International Security and Cooperation
(CISAC) within Stanford's Institute for International
Studies.

Chyba
will devote half his talk to astrobiology -- the
study of the origin, evolution, distribution and
destiny of life in the universe. Astrobiologists
broadly look for life by searching, for example, for
evidence on Mars, Europa and other promising places,
and analyzing comets for organic molecules capable of
seeding life.

Chyba
will devote the other half of his talk to the search
for intelligent life. With other SETI Institute
researchers, Chyba uses the Arecibo radio telescope
in Puerto Rico -- the world's largest at 1,000 feet
across -- to search for a signal. Researchers must
compete for telescope time, and his group gets three
weeks of listening time per year.

"We
are systematically marching through the thousand
nearest sun-like stars looking for artificial
signals," says Chyba, who received his doctorate
in astronomy in 1991 from Cornell University, where
he was a graduate student of Carl Sagan. "We're
more than halfway through that search. That search
has taken about a decade. There are a couple hundred
billion stars in the Milky Way, so looking at the
thousand nearest stars is not likely to be successful
unless the galaxy is replete with extraterrestrial
technical civilizations who are broadcasting."

To cast
a wider net and speed up the search, researchers at
the SETI Institute and the University of
California-Berkeley are building the Allen Telescope
Array in Hat Creek, a radio-quiet part of Northern
California. Listening for signals 24 hours a day,
seven days a week, they will be able to search a
million stars in a decade.

Exploring
the possibility of life in outer space may help us
place ourselves in context in the rest of the
universe and may help us better understand life on
our own planet, Chyba says. "Our increasing
knowledge of life on Earth informs the way we look
for extraterrestrial life. Is there only one way to
make life, or are there many ways? To some extent,
we're starting to answer that question through
experimentation. We've not yet made life in the
laboratory, but we're getting close to that by some
definitions of life in work that's being done in the
so-called RNA world."

The
greater understanding of terrestrial biology that
scientists have gained in the past decade also
informs the search for extraterrestrial microbial
life, Chyba says. "It makes subsurface
environments on Mars and Europa much more
plausible."

Chyba
chaired the team that set science objectives for the
Europa orbiter mission, which aimed to find out if an
ocean exists under the icy surface of that Jovian
moon. That mission never flew due to escalating
costs. While the Galileo spacecraft returned data
strongly suggestive of an ocean, Chyba says
additional measurements are needed to know with
certainty whether an ocean exists under the ice and
to begin to understand Europa's subsurface. NASA is
considering a new mission that would fly to Europa,
as well as Jupiter's moon's Ganymede and Callisto, at
the end of this decade, Chyba says.

Chyba's
research also explores the effects of comet impacts
on the early Earth, as well as Mars and Europa.
Comets potentially deliver so-called biogenic
elements, such as carbon and nitrogen, to the surface
of a world. Since comets may be "extremely
organic-rich, maybe 20 percent by mass," he
says, "it could mean they played an important
role in the origin of life on Earth."

Chyba
will speak more about comets during the technical
component of the Bunyan Lecture, which he will
deliver to faculty and students at 4:15 p.m. Tuesday,
April 22, in Room 201 of the Teaching Center in the
Science and Engineering Quad. His talk is titled
"The Comet-Asteroid Impact Hazard."

The
Bunyan Lecture is named for the late James T. Bunyan,
a member of the Hoover Institution whose will
specified that his estate endow lectures that
"inquire into man's changing vision of the
cosmos and of human destiny as revealed in the latest
discoveries in the fields of astronomy and space
exploration."